tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index bf75c1da4d3e2f98721452037320a82fc75f8899..b047362fec9e4f13363c74ea1a66cba48698bf58 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -250,6 +250,12 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="Android.Activity.ChromeTabbedActivity.StopReason"
+    enum="AndroidActivityStopReason">
+  <owner>dfalcantara@chromium.org</owner>
+  <summary>Why the foreground ChromeTabbedActivity was stopped.</summary>
+</histogram>
+
 <histogram name="Android.ArmFpu" enum="AndroidArmFpu">
   <owner>fdegans@chromium.org</owner>
   <summary>
@@ -57876,6 +57882,15 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="5" label="FullScreenActivity"/>
 </enum>
 
+<enum name="AndroidActivityStopReason" type="int">
+  <int value="0" label="Unknown"/>
+  <int value="1" label="User hit the back button"/>
+  <int value="2" label="User hit the return button"/>

[Ilya Sherman, 2016/02/24 23:01:02]

What's a return button?

[gone, 2016/02/25 01:30:21]

Clarified, hopefully

+  <int value="3" label="Launched a child CustomTabActivity"/>
+  <int value="4" label="Child CustomTabActivity closed itself"/>
+  <int value="5" label="Another Chrome Activity is in the foreground"/>

[Ilya Sherman, 2016/02/24 23:01:02]

It's not entirely clear to me what this case means, in terms of user
interaction.  How did the other activity become foregrounded?

[gone, 2016/02/25 01:30:21]

Is this clearer?

+</enum>
+
 <enum name="AndroidArmFpu" type="int">
   <int value="0" label="No NEON support"/>
   <int value="1" label="NEON support"/>